FireFox has their version of the PDF plug-in and it might not be complete enough to handle the web page you are convertings.

I would try Windows IE 11 with the Acrobat DC converter plug-in. It is not always perfect but it works most of the time.

By the way the majority of responders on this site are not Adobe employees but regular users, so you will not get the attention you might from Adobe Customer Service. All Adobe employees are identified as staff. You have not had any Adobe staff reply to your issue.